callbacks.onSignatureRequest

Replaces the signature dialog, which then never opens. Called by the Sign tool (field is null) and by a form's signature field (field is that field); without the extract feature the field is blanked as formFieldChanged's is. Must resolve with { dataUrl } where dataUrl is a data: URL of a PNG, JPEG, WebP, GIF or BMP image, at most 10 MB. Anything else — null, a web address, SVG, a missing dataUrl — is a cancel, and so is a rejected promise (logged with console.warn). While a request is open, clicking the page or the same signature field again does not ask a second time. If the user switches tool before you answer, the answer is dropped.